A Spatial Sensor Synchronization System Using a Time-Division Multiple Access Communication System

ABSTRACT

A spatial sensor synchronization system using a Time-Division Multiple Access (TDMA) communication system, intended for a plurality of entities evolving inside the TDMA communication system, whereby each one of the plurality of entities is intended to comprise a spatial sensor and a tag enabled to communicate in the TDMA communication system, further whereby each spatial sensor is enabled to make a spatial measurement during a determined active time period, further whereby the tags from the plurality of entities are addressed in sequence by the TDMA communication system with a determined sequence period separating two subsequent addresses in the TDMA communication system. Each of the tags comprises electrical trigger output means configured to output an electrical trigger to the sensor of the corresponding entity at the time of being addressed by the TDMA communication system. Each of the sensors comprises electrical trigger input means connected to the electrical trigger output means, and configured to initiate a spatial sensor measurement for each received electrical trigger. A duration of the determined sequence period is equal or greater than a duration of the determined active time period.

TECHNICAL FIELD

The invention relates to a novel method and system for spatial sensorsynchronization for one or more spatial sensors that are used togetherwith a Time-Division Multiple Access (TDMA) communication system. SuchTDMA communication system may be an Ultra Wide Band (UWB) positioningsystem. Preferably the spatial sensor is a distance measurement oranti-collision sensor.

BACKGROUND

Autonomous robots need at least two inputs to navigate: position tostatic infrastructure and anti-collision sensing for avoiding dynamicobstacles. In a typical application in industry or logistics, therelative positioning system to static infrastructure can be a UWB indoorpositioning system and the collision avoidance functionality can beprovided through the use of Time of Flight (ToF) sensors—at least oneper autonomous robot.

ToF sensors, especially when based on phase measurement principle, cansuffer from false or corrupted measurements due to cross talk between atleast two ToF sensors measuring at the same time, especially when theillumination of the two devices overlap. This is a likely scenario inthe case at least two robots operate in the same static infrastructure.

Systems for crosstalk avoidance exist based on synchronization overcable, an example for an implementation of which can be found inPCT/EP2018/072978. For freely moving robots this method is notapplicable, a wireless solution as described above is necessary.

Departing from the known systems as described above, one aim of thepresent invention is to find a method and a system that prevent false orcorrupted measurements.

SUMMARY OF THE INVENTION

The invention provides a spatial sensor synchronization system using aTime-Division Multiple Access (TDMA) communication system, intended fora plurality of entities evolving inside the TDMA communication system,whereby each one of the plurality of entities comprises a spatial sensorand a tag enabled to communicate in the TDMA communication system,further whereby each spatial sensor is enabled to make a spatialmeasurement during a determined active time period, further whereby thetags from the plurality of entities are addressed in sequence by theTDMA communication system with a determined sequence period separatingtwo subsequent addresses in the TDMA communication system. Each of thetags comprises electrical trigger output means configured to output anelectrical trigger to the sensor of the corresponding entity at the timeof being addressed by the TDMA communication system. Each of the sensorscomprises electrical trigger input means connected to the electricaltrigger output means, and configured to initiate a spatial sensormeasurement for each received electrical trigger. A duration of thedetermined sequence period is equal or greater than a duration of thedetermined active time period.

In a preferred embodiment of the invention, the spatial sensor is adistance measurement or anti-collision sensor.

In a further preferred embodiment, the TDMA communication system is anUltra Wide Band (UWB) system.

In a further preferred embodiment, the spatial sensor is a Time ofFlight (ToF) sensor, and the TDMA communication system is an Ultra WideBand (UWB) system.

In a further preferred embodiment, at least one of the plurality ofentities is intended to comprise at least an additional ToF sensor, andthat the additional ToF sensor is also triggered by the receivedelectrical trigger.

In a second aspect, the invention provides a method for spatial sensorsynchronization for one or more spatial sensors that are used togetherwith a Time-Division Multiple Access (TDMA) communication system. Eachspatial sensor is enabled to make a spatial measurement during adetermined active time period. The method comprises steps of: the one ormore spatial sensors connects to the TDMA system; the TDMA systemaddresses the one or more spatial sensors with a determined sequenceperiod separating two subsequent addresses in the TDMA communicationsystem, the one or more spatial sensors extracts a timing signal at atime of being addressed by the TDMA system; the one or more spatialsensors aligns to the timing signal; use the timing signal as a triggersignal to trigger one or a series of spatial sensors from the one ormore spatial sensors for measuring; whereby a duration of the sequenceperiod is equal or greater than a duration of the determined activeperiod; and repeating the method by starting again at the step of theone of more spatial sensors connecting to the TDMA system.

In a further preferred embodiment, at the step in which the one or morespatial sensors aligns to the timing signal, the one or more spatialsensors waits for the timing signal to arrive.

In a further preferred embodiment, at the step in which the one or morespatial sensors aligns to the timing signal, an internal clockrespectively of the one or more spatial sensors synchronizes with thetiming signal, and each one of the one or more spatial sensors waits apredefined time before measuring.

In a further preferred embodiment, prior to implementing the step of theone or more spatial sensors extracting a timing signal, the methodfurther comprises a step of shaping and sending the timing signal by theTDMA device such that it provides right electrical characteristics for atrigger input of each respective one or more spatial sensors.

In a further preferred embodiment, the step of using the timing signalfurther comprises a step of providing the one or more spatial sensors ina daisy chain, whereby each spatial sensor receives, delays and re-emitsthe trigger signal, whereby each spatial sensor delays such that nocrosstalk from measurements occurs.

In a further preferred embodiment, the step of using the timing signalfurther comprises a step of providing the one or more spatial sensors ina star topology of spatial sensors where each one of the spatial sensorsreceives the trigger signal at the same time and each one of the spatialsensors delays a start of the measuring by a different amount of timechosen such that no crosstalk from measurements occurs.

In a further preferred embodiment, the step of using the timing signalfurther comprises a step of providing the one or more spatial sensors ina sensor hub with the one or more spatial sensors connected to it, thesensor hub being configured to implement a step of determining ameasurement sequence for the one or more spatial sensors in such a waythat no crosstalk from measurements occurs.

In a further preferred embodiment, the sensor hub is further configuredto implement a step of optimizing a measurement speed depending on ageometrical configuration of the one on more spatial sensors.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be explained through the description of preferredembodiments, and in reference to the drawings, wherein

FIG. 1 illustrates an example system comprising a plurality of robotsand a target intended to illustrate a problem addressed by theinvention;

FIG. 2 schematically illustrates an example embodiment of a systemaccording to the invention;

FIG. 3 schematically illustrates an internal configuration of anautonomous robot according to an example embodiment of the invention;

FIG. 4 contains a timing diagram for an example system according to theinvention; and

FIG. 5 contains a flowchart illustrating an example implementation ofthe method according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates the problem that is overcome by the use of thepresent invention. Each of a plurality of autonomous robots (2, 3) usesan active sensing technology with an active sensor 3 that may interferein case of simultaneous measurement. In the case in which at least tworobots measure and point to a same target 4 at the same time,interference may appear and lead to erroneous measurements and in somecases accidents or lost navigation. In the case each of the robots isequipped with an UWB-based absolute positioning system 2, the inventionprovides a method of synchronizing the measurements of the activesensors 3 in such way that no interference occurs.

In one preferred embodiment the present invention departs from two priorart technologies, namely UWB positioning (see for example referencePMC4883398) and Time-of-Flight (ToF) sensors.

ToF sensors work in a pulsed manner according to the following 2 phases:

-   -   an active phase where a signal is sent out and its reflection        from a target is received at the same time; and    -   a passive phase where the received signal is treated, calibrated        and communicated.

The active phase is typically short compared to the passive phase,nevertheless it is in the active phase that crosstalk may occur asexplained hereafter: if in a first ToF sensor that sent out a signalthat is reflected from the target and received in the first ToF sensor,one of the signals from another ToF sensor is also received in the firstToF, in superposition.

UWB systems typically comprise a number of UWB transceivers fixed to thestatic infrastructure in known positions (called ‘anchors’) and portableUWB transceivers (called ‘tags’) that communicate with the anchors andcalculate their relative position to the anchors and therefore to thestatic infrastructure using the Time Difference Of Arrival (TDOA)principle (See for example reference Multilateration). Since only onetag at a time can communicate with the anchors, the system is timed in asequential way where one tag after the other communicates with theanchors to calculate its position (Time-Division Multiple Access (TDMA)principle, each tag has its own ‘slot’, see for example referenceTime-division_multiple_access). Once all tags have finished calculatingtheir position, the system starts over (system loop cycle time,typically ˜100 ms).

The idea underlying to the method and system according to the inventionis to use the internal timing of the UWB system to trigger themeasurements of the ToF sensors.

A preferred embodiment of the system according to the inventioncomprises:

-   -   the UWB system which comprises an electrical trigger output on        each tag, and is further configured such that each time a tag        manages to calculate a valid absolute or relative position, it        will output an electrical trigger output pulse. Preferably a        configuration may be realized by means of a firmware        modification in a conventional prior art UWB system;    -   an electrical connection between the UWB tag and ToF sensor or        ToF sensor hub inside an entity carrying both tag and sensor,        such as for example a robot; and    -   the ToF sensor or ToF sensor hub, which comprises an electrical        trigger input and adapted firmware to receive and handle the        internal triggering.

Given the TDMA principle, all trigger pulses from all tags in the systemwill occur sequentially with a minimum time between those, thus leavingtime for each attached ToF system to finish a ToF measurement withoutthe risk of crosstalk with other systems. Preferably the minimum time isequal or greater than a duration of the active phase of the ToF system.

Referring to FIG. 2, which schematically illustrates an exampleembodiment of a system according to the invention, the system comprisestwo main subsystems. The first main subsystem comprises the autonomousrobots (2, 3) each with integrated active sensors 3. The second mainsubsystem comprises UWB transceivers or ‘tags’ 2 and UWB anchors 1.While the UWB anchors 1 are fixed in space, the autonomous robots (2, 3)may move in space and use their active sensors 3 for anti-collision andnavigation purposes.

FIG. 3 illustrates the internal configuration of an autonomous robotaccording to a preferred embodiment and configured to allowanti-interference operation according to the present invention. Theinternal configuration comprises an active sensor 3 a with a connection3 b to a robot control system 4 a. The connection 3 b transports sensordata to the control system 4 a to enable navigation and anti-collisionfunctions. In addition, an UWB tag 2 a together with its receptionantenna 2 b and data connection 2 c for forwarding of positioninformation to the robot control system 4 a is part of the system. Theinventive system further comprises an additional, direct connection 2 bbetween the UWB tag 2 a and the active sensor 3 a. The connection 2 bprovides synchronization pulses from the UWB tag 2 a to the activesensor 3 a to allow interference-free operation of the active sensors inthe case of multiple robots operating within the range of the activesensors 3 a.

FIG. 4 shows a timing diagram of the system. Line 1 is the TDMAcommunication between UWB anchors and tags (both not shown in FIG. 4).Each pulse in line 1 illustrates a navigation message between theanchors and one tag (typically on an autonomous robot). The system (notshown in FIG. 4) is managed in such a way that there is always only onetag communicating at the time, one after the other. Once all tags havefinished communicating the system starts over. Lines 2 and 3 show outputpulses of the UWB tags embedded in the autonomous robots. These outputpulses are derived from the TDMA pulses and are transmitted viaconnection 2 b shown in FIG. 3, to the active sensors 3 a also shown inFIG. 3. These pulses then trigger the measurement of the active sensors,the active sensing phases are shown in lines 4 and 5. In the case thatthe time between two TDMA pulses is longer than the active sensing timeof the active sensors plus the inherent system delays (pulse selectionand transmission), no interference of the active sensors will occur evenon comparatively long time scales.

More generally, the invention is not restricted to the use of ToF assensors, including 3D cameras and other active sensors based on the ToFprinciple. Instead other sensors potentially suffering crosstalk at thetime of measurement may also be used, such as distance measurementsensors and anti-collision sensors based on ultrasound ranging. It mayeven be possible to make use of a variety of sensor types together,whereby crosstalk may or may not occur between each variety of sensortypes.

Further, the invention is not either restricted to make use of a UWBsystem. More generally, any Time-Division Multiple Access communicationsystem being used in common by a plurality of entities carrying one ofthe variety of sensors is suitable to implement the invention, as longas the TDMA system attributes a corresponding tag to each one of theplurality of entities and the tag may be adapted to work in a mannersimilar to that described for the embodiments using UWB tags and ToF.

Referring now to FIG. 5, this illustrates by means of a flowchart anexample of a method for spatial sensor synchronization for one or morespatial sensors that are used together with a Time-Division MultipleAccess (TDMA) communication system. FIG. 5 shows the following steps:

Box 51: the one or more spatial sensors connects to the TDMA system;

Box 52: the one or more spatial sensors extracts a timing signal from aTDMA device's output signal after having addressed the TDMA devicewithin the TDMA system;

Box 53: the one or more spatial sensors aligns to the timing signal;

Box 54: use the timing signal as a trigger signal to trigger one or aseries of spatial sensors from the one or more spatial sensors formeasuring; and

Arrow line 55: repeat the method by starting again at the step of box51.

In a preferred embodiment, the step of box 53, i.e., the step in whichthe one or more spatial sensors aligns to the timing signal, the actionof «aligns » may be understood as a synchronization. In this step thesensor ‘waits’ for the timing signal to arrive. In a further preferredembodiment, the action of «aligns » means that an internal clock of thesensor gets synced with the timing signal and then the sensor waits apredefined time before measuring.

In a further preferred embodiment, the step of box 52 is preceded by afurther step, wherein the timing signal is shaped and sent by the TDMAdevice such that it provides the right electrical characteristics for atrigger input of each respective one or more spatial sensors.

In a further preferred embodiment, the step of «use the timing signal »in box 54 involves providing the one or more spatial sensors in a daisychain, whereby each spatial sensor receives, delays and re-emits thetrigger signal, whereby each spatial sensor delays such that nocrosstalk from measurements occurs. This is for example explained withrespect to the timing diagram of FIG. 4.

In a further preferred embodiment, the step of «use the timing signal »in box 54 involves providing the one or more spatial sensors in a startopology of spatial sensors where each one of the spatial sensorsreceives the trigger signal at the same time and each one of the spatialsensors delays a start of the measuring by a different amount of timechosen such that no crosstalk from measurements occurs.

In a further preferred embodiment, the step of «use the timing signal »in box 54 involves providing the one or more spatial sensors in a sensorhub with the one or more spatial sensors connected to it. The sensor hubis configured to implement a step of determining a measurement sequencefor the one or more spatial sensors in such a way that no crosstalk frommeasurements occurs. In an further preferred embodiment, the sensor hubis further configured to implement a step of optimizing a measurementspeed depending on a geometrical configuration of the one on morespatial sensors.

References

PMC4883398

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4883398/

Multilaterations

https://en.wikipedia.org/wiki/Multilateration

Time-division_multiple_access

https://en.wikipedia.org/wiki/Time-division_multiple_access

1-13. (canceled).
 14. A spatial sensor synchronization systemcomprising: a Time-Division Multiple Access (TDMA) communication system;and a plurality of movable devices moving within TDMA communicationsystem, each movable device including a spatial sensor and a tag that isconfigured to communicate within the TDMA communication system, whereineach spatial sensor is configured to perform a spatial measurementduring a determined active time period, wherein each tags are addressedin sequence by the TDMA communication system with a determined sequenceperiod separating two subsequent addresses in the TDMA communicationsystem, wherein each tag includes a trigger output device configured tooutput an electrical trigger to the spatial sensor of the correspondingmovable device, after being addressed by the TDMA communication system,wherein each spatial sensor includes a trigger input device connected tothe trigger output device of the corresponding tag, the trigger inputdevice configured to initiate a spatial sensor measurement a receivedelectrical trigger, and wherein a duration of the sequence period isequal or greater than a duration of the determined active time period.15. The system of claim 14, wherein the spatial sensor is a distancemeasurement or anti-collision sensor.
 16. The system of claim 14,wherein the TDMA communication system includes an Ultra Wide Band (UWB)system.
 17. The system of claim 14, wherein the spatial sensor includesa Time of Flight (ToF) sensor, and the TDMA communication systemincludes an Ultra Wide Band (UWB) system.
 18. The system of claim 17,wherein at least one of the plurality of movable devices includes anadditional ToF sensor, and the additional ToF sensor also configured tobe triggered by the received electrical trigger.
 19. A method forsynchronizing of a spatial sensor that is used together with aTime-Division Multiple Access (TDMA) communication system, the spatialsensor configured to make a spatial measurement during an active timeperiod, the method comprising the steps of: connecting the spatialsensor to the TDMA communication system; addressing the spatial sensorwith a sequence period, the sequence period separating two subsequentaddresses in the TDMA communication system, a duration of the sequenceperiod being equal to or greater than a duration of the active timeperiod; extracting a timing signal by the spatial sensor after the stepof addressing; aligning the spatial sensor to the timing signal; usingthe timing signal as a trigger signal to trigger the spatial measurementby the spatial sensor and/or one or more additional spatial sensors; andrepeating the steps of connecting, addressing, extracting, aligning, andusing.
 20. The method of claim 19, wherein in the step of aligning, thespatial sensor aligns to the timing signal, while the one or moreadditional spatial sensors wait for the trigger signal to arrive. 21.The method of claim 19, wherein in the step of aligning, an internalclock of the spatial sensor synchronizes with the timing signal, the oneor more additional spatial sensors wait a predefined time period beforeperforming the spatial measurement.
 22. The method of claim 19, whereinthe method further comprises a step of: shaping and sending the timingsignal by the TDMA communication system such that the timing signal hascorrect electrical characteristics for each one of the spatial sensors,before the step of extracting the timing signal.
 23. The method of claim19, wherein the step of using the timing signal further comprises a stepof providing the spatial sensor and/or one or more additional spatialsensors in a daisy chain, wherein each spatial sensor receives, delaysand re-emits the trigger signal, the delays being such that no crosstalkfrom the spatial measurements occurs.
 24. The method of claim 19,wherein the step of using the timing signal further comprises a step ofaddressing the one or more additional spatial sensors in a startopology, wherein each one of the additional spatial sensors receivesthe trigger signal at the same time and each one of the additionalspatial sensors delays a start of the spatial measurement by a differentamount of time chosen such that no crosstalk from the spatialmeasurements occurs.
 25. The method of claim 19, wherein the step ofusing the timing signal further comprises a step of arranging the one ormore additional spatial sensors in a sensor hub, the sensor hub beingconfigured to implement a step of determining a measurement sequence forthe one or more spatial sensors in such a way that no crosstalk from thespatial measurements occurs.
 26. The method of claim 25, wherein thesensor hub is further configured to perform a step of optimizing ameasurement speed depending on a geometrical configuration of the one onmore additional spatial sensors.